Peter K. L. Ng’s research while affiliated with New Mexico Museum of Natural History and Science and other places

The identities of three brachyuran taxa, Parapleurophrycoides , Parapleurophrycoides roseus and Platyozius perpusillus , newly established by Nobili (1906a) are clarified. The new genus and new species descriptions were based on juveniles from Marutea South in French Polynesia, consequently their taxonomy has been problematic. The only known illustration of Parapleurophrycoides roseus by Nobili (1906b) is small and schematic, while Platyozius perpusillus has never been figured. While various authors have speculated on their taxonomy, others just treat them as nomina dubia. The present study re-examines and figures the types of the two species. While the specimens are small and in poor condition, there are nevertheless enough characters to clearly indicate their familial assignment. Parapleurophrycoides (and its type species, Parapleurophrycoides roseus ) is here shown to be closely allied to Viaderiana Ward, 1942, in the Pilumnidae Samouelle, 1819; while Platyozius perpusillus is assigned to the Chlorodiellinae Ng & Holthuis, 2007, in the Xanthidae MacLeay, 1838, although it is not possible to place it in any known genus.

The goneplacid crab, Carcinoplax mistio Ng & Mitra, 2019, was originally described from West Bengal, India, in the northern Indian Ocean. Additional material of C. mistio from off Tamil Nadu in the southeast of India revealed a high degree of size-associated variation in the structures of the anterolateral tooth of the carapace, chelipeds, and male and female pleons. In addition to an in-depth morphological examination of C. mistio, this study also records the natural coloration of the species and conducts a genetic comparison (with mitochondrial COI and 16S rRNA genes) with its close relatives, C. haswelli (Miers, 1884) and C. purpurea Rathbun, 1914. Molecular comparison of C. mistio with its morphologically closest congener, C. haswelli from northern Australia and the western Pacific, corroborates their status as separate species. The genetic sequence of C. mistio, however, is similar to that of C. purpurea from the West Pacific, although these two species can easily be distinguished by distinct carapace and ambulatory leg characters. The present study provides some possible explanations for the genetic and morphological incongruence observed between C. mistio and C. purpurea and highlights the need for a detailed molecular study for Carcinoplax H. Milne Edwards, 1852, to appreciate the evolution of various morphological characters in the genus.

The precise identity of the potamid freshwater crab, Indochinamon beieri (Pretzmann, 1966), is ascertained, diagnosed and illustrated after examining the type material from Myanmar. The diagnosis/description of the species and subsequent accounts were based on a wrongly identified and illustrated specimen, probably from Nagaland in northeastern India, which caused substantial confusion among carcinologists, who referred to different taxa as I. beieri. Two such taxa from northeastern India are referred to herein as new species of a new genus, Capitamon n. gen., i.e., C. mizoramense n. gen., n. sp. from Mizoram and C. clarki n. gen., n. sp. probably from Nagaland. Capitamon n. gen. also includes two new species, i.e., C. capitatum n. gen., n. sp. (type species) from Arunachal Pradesh and Nagaland, and C. meitei n. gen., n. sp. from Manipur. Indochinamon manipurense (Alcock, 1909) is also assigned to Capitamon n. gen. as it possesses the characteristics of the new genus. Capitamon n. gen. is thus known by five nominal species from northeastern India, while I. beieri is restricted to its type locality in Myanmar, with the previous Indian records revealed to be erroneous. With the exclusion of I. manipurense, Indochinamon Yeo & Ng, 2007, now contains 42 species. An identification key to the species of Capitamon n. gen. is provided.

A new species of pilumnid crab, Pseudolitochira spinosa sp. nov., is described from a seagrass bed in Panglao, Bohol, central Philippines. The new species is morphologically most similar to P. maenosonoi Ng & Clark, 2022, from Okinawa, Japan, in its proportionately wide carapace, but can be distinguished by the possession of prominent anterolateral spines, distinct spines on the merus of the cheliped and the presence of a well-developed sharp tooth on the inner angle of the cheliped carpus. The taxonomy of the poorly known P. setosa (A. Milne-Edwards, 1873) from New Caledonia is also discussed and a lectotype selected.

A second species of the previously monotypic aphanodactylid crab genus Gustavus Ahyong & Ng, 2009 is described from the Red Sea coast of Saudi Arabia. The new species, Gustavus holthuisae sp. nov., inhabits the tubes of terebellid polychaetes near mangrove roots. It can be distinguished from the type species from Guam, Gustavus mecognathus Ahyong & Ng, 2009, by the structure of the dorsal surface of the carapace, the proportions and form of the frontal margin, the shape of the third maxilliped, the armature of the basis-ischium and merus of the third and fourth ambulatory legs, and the structure of the male pleon and gonopods.

Camptoplax ahmar sp. nov. is described based on a single male specimen extracted from a burrow of an unknown host near Thuwal, Red Sea coast of Saudi Arabia. The new species differs from the type-species of Camptoplax Miers, 1884 and its only congener, C. coppingeri Miers, 1884, by several morphological / morphometric details.

Nepinnotheres villosulus (Guérin-Méneville, 1832) [Guérin-Méneville, 1829–1837] [type locality: Timor] and Nepinnotheres edwardsi (De Man, 1887) [type locality: Mergui Archipelago], as currently understood, are both reportedly widespread in Southeast Asia and northern Australia, and unique in the genus in having females densely covered by a setal tomentum that completely obscures the surfaces of the carapace and pereiopods. Based on the limited information contained in the type accounts, N. edwardsi and N. villosulus appear indistinguishable, but this cannot currently be confirmed by comparing type material because the holotype of N. villosulus, the senior name, is lost. A neotype is therefore designated for N. villosulus to fix its identity and taxonomic status as a senior synonym of N. edwardsi. In addition to the unique setation pattern of female N. villosulus, males of the species also present important differences from those of male Nepinnotheres sensu stricto. Pinnotheres trichopusTesch, 1918 [type locality: Elat, Great Kei Island, Indonesia], is also shown to be a junior synonym of P. villosulus. Moreover, recent molecular phylogenetic analyses determined that N. villosulus is phylogenetically distant from Nepinnotheres sensu stricto. As such, we establish a new genus for N. villosulus.

Three species of Geosesarma : G. celebense , G. leprosum and G. clavicrure have been previously described from the Indonesian island of Sulawesi. To evaluate their identities, we examined type material of the three species, and they are re-described and illustrated. A short segment of 229 bp of COX1 gene from the Sulawesian Geosesarma was obtained (when available) and used for genetic comparisons. Our record of G. celebense from Selatan, South Sulawesi, and the genetic affinity between the type from North Sulawesi and the southern material indicates that G. celebense is well distributed throughout Sulawesi. The present study also describes a new species of Geosesarma from central Sulawesi. Geosesarma schubarti new species differs significantly from other Sulawesian Geosesarma in the morphology of the carapace, which is distinctly squarish in shape with a clear second anterolateral tooth. Genetic distances, using the segment of COX1 marker, showed all Sulawesian Geosesarma species, including the new one, are distant from each other. Our morphological comparisons also show that G. clavicrure is actually a junior subjective synonym of Bresedium brevipes ; and the sequences of G. clavicrure grouped stably with B. brevipes in the 16S phylogenetic tree, and G. clavicrure therefore needs to be removed from the genus Geosesarma . As a consequence, with the new species, there remain three known species for Sulawesi ( G. celebense , G. leprosum , G. schubarti ), but based on currently available evidence it is considered likely that there exist additional species from this genus on the island.